Lab-2
2-MAKING PROGRAM COUNTER
The purpose of this lab is to make circuit of Program Counter of SAP-1 which generates a 4-bit address
code of memory.
Components Required
• Dual J-K Flip Flop, 74LS107------------(2)
• Quad Tri-state Switch, 74LS126-------(1)
• Connecting Wires
What is Program Counter?
The program counter, which is a part of control unit, counts according to the available RAM-memory .Its
job is to send to the memory the address of the next instruction to be fetched and executed. Program
counter is also called pointer, as it works like pointing at a list of instructions stored at different addresses
in the memory, saying do this first, do this second etc.
Program Counter for SAP-1
Chips C1, C2 and C3 when connected as shown in the circuit are serving as the program counter.
Chip C1, a 74LS107, is a dual J-K flip flop that produces the upper 2 address bits. Chip C2, another
74LS107, produces the lower 2 address bits. Chip C3 is a 74LS126, a quad tri-state normally open
switch, it gives the program counter a three state output. At the start of the computer run, a low CLR
resets the program counter to 0000. During the T1 state, a high Ep latches the address on W bus. During
the T2 state, a high Cp is applied to program counter, midway through this state, the negative CLR edge
increments the program counter. The program counter is inactive during T3 to T6 states.
Procedure
Connect the circuit as shown in the figure.
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